docs: def _compute_f0_factor(self, rrup):
          """
          Compute and return factor f0 - see equation (5), 6th term, p. 2191.
          """
          # f0 = max(log10(R0/rrup),0)
          f0 = np.log10(self.COEFFS_IMT_INDEPENDENT['R0'] / rrup)
          f0[f0 < 0] = 0.0
  
          return f0